1. Field of the Invention
The present invention relates to a fuel supply apparatus for an internal combustion engine having a plurality of cylinders, which supplies fuel through fuel injection valves, and particularly to a fuel supply apparatus which performs the fuel injection in which fuel injection periods corresponding to a plurality of cylinders overlap with each other in a specific operating condition of the engine.
2. Description of the Related Art
Japanese Patent Laid-open No. H03-74548 (JP'548) discloses a fuel supply apparatus which performs correction according to a pressure of fuel supplied to a fuel injection valve (fuel pressure) in order to estimate an amount of fuel injected by the fuel injection valve with sufficient accuracy. In the fuel supply apparatus for the internal combustion engine shown in JP'548, two fuel injection modes are adopted, i.e., one is a sequential injection mode and the other is a group injection mode in which the fuel injections are simultaneously performed with respect to two cylinders. The fuel injection amount is estimated taking the following two points into consideration: one point is that the flow rate of fuel consumed in one combustion changes depending on the fuel injection mode, and the other point is that the fuel flow rate changes depending on a pressure difference between the fuel pressure and the intake pressure.
JP'548 suggests the above-described method for estimating the fuel injection amount with sufficient accuracy. However, no technique for controlling the fuel injection amount to a desired value with sufficient accuracy is shown in JP'548. Further, changes in the fuel pressure during the period in which the fuel injection valve opens are not taken into consideration. Therefore, it is difficult to accurately control the fuel injection amount especially in the group injection mode, only by using the technique shown in JP'548.